Wireless communication systems compliant with Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) may support up to 100 Mbps in the downlink (DL), and up to 50 Mbps in the uplink (UL) for a 2×2 configuration. The LTE DL scheme may be based on an Orthogonal Frequency Division Multiple Access (OFDMA) air interface. For the purpose of flexible deployment, wireless communication systems may support scalable transmission bandwidths, which may be one of 1.4, 3, 5, 10, 15 or 20 MHz. Each radio frame (for example, 10 ms) may consist of ten subframes of 1 ms each. Each subframe may consist of two timeslots of 0.5 ms each. There may be either seven or six Orthogonal Frequency Division Multiplexing (OFDM) symbols per timeslot. Seven symbols per timeslot may be used with normal cyclic prefix (CP) length, and six symbols per timeslot may be used with the extended CP length. The sub-carrier spacing for a particular specification is 15 kHz. A reduced sub-carrier spacing mode using 7.5 kHz may also be possible.
A resource element (RE) may correspond to one sub-carrier during one OFDM symbol interval. Twelve consecutive sub-carriers during a 0.5 ms timeslot may constitute one resource block (RB). With seven symbols per timeslot, each RB may consist of 12×7=84 REs. A DL carrier may consist of 6 RBs to 110 RBs which may correspond to an overall scalable transmission bandwidth of roughly 1 MHz to MHz. Each transmission bandwidth, for example, 1.4, 3, 5, 10 or 20 MHz, may correspond to a number of RBs.
The basic time-domain unit for dynamic scheduling may be one subframe consisting of two consecutive timeslots. This may sometimes be referred to as a RB pair. Certain subcarriers on some OFDM symbols may be allocated to carry pilot or reference signals in the time-frequency grid. A number of subcarriers at the edges of the transmission bandwidth may not be transmitted in order to comply with spectral mask requirements.
In single carrier configuration for frequency division duplex (FDD), the network may assign a wireless transmit/receive unit (WTRU) one pair of UL and DL carriers. In single carrier configuration for time division duplex (TDD), the network may assign one carrier which may be time shared for UL and DL. For a given WTRU for any given subframe, there may be a single Hybrid Automatic Repeat reQuest (HARQ) process active for the UL and a single HARQ process active in the DL.
Carrier Aggregation (CA) provides an evolution from single carrier operation that aims to improve data rates using, among other solutions, bandwidth extensions. With CA, the WTRU may simultaneously transmit over the Physical Uplink Shared CHannel (PUSCH) or receive over the Physical Downlink Shared CHannel (PDSCH) of multiple serving cells. For example, in a wireless communication system such as an LTE-Advanced (LTE-A) system, up to four secondary serving cells (SCells) may be used in addition to a Primary serving Cell (PCell), enabling flexible bandwidth assignments up to 100 MHz. Uplink Control Information (UCI), which may consist of HARQ ACK/NACK feedback and/or Channel State Information (CSI), may be transmitted either on Physical Uplink Control CHannel (PUCCH) resources of the PCell or on PUSCH resources available for a serving cell configured for uplink transmissions.
The control information for the scheduling of PDSCH and PUSCH may be transmitted on one or more Physical Downlink Control CHannel(s) (PDCCH) or enhanced PDCCH (EPDCCH). Scheduling for a serving cell may be via a DL control channel on the same serving cell. In addition, when operating with CA, cross-carrier scheduling may also be supported, which may allow the network to use a DL control channel on one serving cell to provide PDSCH assignments and/or PUSCH grants for transmissions in other serving cell(s).